This reverts commit d390e24c49ba8543b56948402622563cae6e860f.
Forcing tests to success is really bad idea. It'll only lead to cases when
you see PASSED and will think everything is OK.
Long story short: never force tests to pass!
The idea is to use the set of really small images from the lib folder
and run Cycles render on them comparing render output to reference
images in the tests repository.
For sure same thing could become more generic for BI or Freestyle
render engines.
Thanks Campbell for review and code tweaks!